1. Field of the Invention
This invention relates in general to magnetic transducers for reading information signals from a magnetic medium, and in particular, to an improved magnetoresistive read transducer.
2. Description of the Prior Art
The prior art discloses a magnetic transducer referred to as magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at high linear densities. An MR sensor detects magnetic field signals through the resistance changes of a read element made from a magnetoresistive material as a function of the amount and direction of magnetic flux being sensed by the element.
In the past, principal problems with the MR sensors of unstable operating characteristics have limited their use. One of the sources of unstable operating characteristics has been the conductive lead structures by which resistance variations of the MR film have been sensed. The conductive lead structures have comprised the well-known low resistivity materials which are good electrical conductors. For example, U.S. Pat. No. 4,622,613 to Nomura, et al. describes an MR sensor in which the conductive lead structures are formed of copper, gold, and silver. U.S. Pat. No. 4,663,684 to Kamo, et al. describes an MR sensor in which the conductive lead structures are formed of gold or aluminum.
Other conductive lead structures have utilized multi-layer configurations. U.S. Pat. No. 4,503,394 discloses an MR sensor in which the conductive lead structure are formed of a two-layer assembly in which the first layer is made from a material selected from the group consisting of Cr, Mo, and Ti and the second layer is made from a material selected from the group consisting of Al, Au, Pt and Pd. U.S. Pat. No. 4,914,538 discloses an MR sensor having a lead structure comprising a thin film of tungsten having a thin film overlayer, or, alternatively, a thin film overlayer and a thin film underlayer, with both the thin film overlayer and the thin film underlayer formed of a material taken from the group consisting of Ti, Ta, Cr, Zr, Hf and TiW.
In the MR conductor lead application, the materials face much more stringent requirements when compared to other interconnect conductors, such as for semiconductor devices, for example. This is because the conductor lead is exposed at the slider air bearing surface and therefore has little protection from the severe mechanical environment where head-disk contact occurs frequently and the severe corrosion environment where chemical attack occurs both during processing and also in actual use where the environment may not be well controlled.
What is required in the MR conductor lead application is a structure which has not only low resistivity but also excellent resistance to corrosion and which maintains these characteristics without change for an extended period of usage.